Refrigeration system defrosting by controlled flow of gaseous refrigerant



Sept. 14, 1954 c. L. WHITE REFRIGERATION SYSTEM DEFROSTING BY CONTROLLED FLOW OF GASEOUS REFRIGERANT Filed April 2, 1951 lllll RECEIVER saw J23? 1N VENTOR gyl.

BY M ATTUR If;

Patented Sept. 14, 1954 REFRIGERATION SYSTEM DEFROSTING BY CONTROLLED FLOW 'OF GASEOUS RE- FRIGERANT Causey L. White, Atlanta, Ga., assignor to Larkin Coils, Inc., Atlanta, Ga., a corporation of Georgia Application April 2, 1951, Serial N 0. 218,834

3 Claims. 1

This invention relates to mechanical refrigeration systems of that type in which the defrosting of the surfaces of the evaporator is accomplished by the periodic replacement of cold refrigerant in the evaporator by hot refrigerant gas from the compression side of the compressor. This hot refrigerant is generally supplied to the evaporator by way of a valve controlled branch conduit which taps the line from the high pressure side of the compressor to the condenser.

One of the drawbacks of this method of defrosting is that some of the hot refrigerant gas, contacting the cold interior surfaces of the evaporator, condenses into liquid form. If the rate of accumulation of this liquid is uncontrolled, it becomes a definite hazard to the compressor, since it may drain back into the compression chamber either through the branch conduit or be carried over into the suction line.

The liquid being incompressible, is apt to break the piston or other parts of the compressor. The hazard is particularly heavy in those systems in which the evaporator is called upon to maintain a below freezing temperature in the refrigerated chamber.

The problem of protecting the compressor from the inflow of refrigerant in liquid form from the evaporator has been recognized and measures have been proposed for its solution, such as arranging an auxiliary heater in heat exchanging relation to the branch conduit to evaporate the liquid refrigerant as it drains back throughthe branch conduit, before it reaches thecompressor, or to put a check valve in the branch conduit to prevent the return of liquid by the path, permitting it to slug over into the suction line, and to place a heater in heat exchanging relationship to the suction line ahead of the compressor. Any expedient for supplying auxiliary heat to evaporate the otherwise uncontrolled excess of liquid refrigerant used in defrosting amounts to inefiiciency, involving the work done in compressing the refrigerant which becomes condensed in the evaporator and the energy supplied to the heater in nullifying this work.

The present invention has for its object to prevent the condensation of a hazardous amount of liquid in the evaporator by limiting the flow of hot gaseous refrigerant to the evaporaton'to the extent that it cannot condense into a greater 7 amount of liquid than will be completely evaporated by the hot gas in the branch conduit, as the liquid flows contracurrentwise to the hot gas in said conduit. The provision of a metering orifice precisely sized with respect to the refriger- 2 ating capacity of a particular evaporator is employed in carrying out the invention.

Other objects of the invention will appear as the following description of a preferred and practical embodiment thereof proceeds.

In the drawing which accompanies and forms a part of the following specification:

Figure 1 is a diagrammatic layout of a refrigeration system embodying the principles of the invention;

Figure 2 is a cross-section through a T fitting in which the orifice is incorporated.

Referring now in detail to the drawing, the rectangle I, designated by the broken lines represents a refrigerated chamber, preferably one in which the temperature is maintained below 32. Within said chamber is the evaporator 2, below which is the pan 3 for catching the water resulting from defrosting, said pan discharging through a pipe 4, which extends to a point 5 outside of the refrigerated chamber. Beneath the evaporator is a baffle 6. which inclines downwardly toward the inlet end of the discharge pipe t. A fan I, driven by the motor 8, circulates air through the evaporator and throughout the refrigerated chamber.

Outside of the refrigerated chamber is the compressor 9, connected to the upper part of the evaporator by the suction pipe I0 and to the condenser II by the hot compressed gaseous refrigerant pipe I2. The condenser is connected at its lower end to the receiver I3, the receiver being connected by the liquid refrigerant pipe I4 through the expansion valve I5 to the lower part of the evaporator. The compressor is driven by the motor I6. In the system as illustrated, the liquid refrigerant pipe I4 passes in heat exchanging relationship to the suction pipe ID in a heat exchanger H, where the liquid is cooled by the gas in the suction line, whereby its refrigerating efiiciency is somewhat enhanced.

For the purpose of defrosting, a branch conduit I8 leads from the hot gaseous refrigerant pipe I2 at a point between the compressor and condenser to the pipe I5 adjacent the evaporator, lay-passing the expansion valve. For convenience, there is a cutoff valve l9 at the lower end of the branch conduit I8, which is normally left open. At some point in the branch, conduit I3, preferably near its connection with the pipe i5, there is a normally closed solenoid valve 20. Since the baflie 6 and discharge pipe 4 within the refrigerated chamber are constantly within a freezing atmosphere, they are heated to keep the defrost water liquid until it reaches the outside of the refrigerated chamber. For heating the discharge pipe 4, the branch conduit [8 is substantially in heat exchanging relationship to the discharge pipe throughout that part of its extent which is within the refrigerated chamber. An electric heater 2| is shown in heat exchanging relationship to the baille 6.

The expansion valve l5 operates responsive to a thermostatic bulb 22 against the suction line adjacent the efiiuent end of the evaporator.

Defrosting is automatically accomplished at timed intervals by means of the defrost control 23, which controls the circuits of the fan motor 8, the compressor motor I6, the electric heater 2|, and the solenoid valve 20. The frost control also contains a timer. When the time for defrosting arrives, the following functions take place. The compressor is started, if it is not already running at the time, to supply hot gas under pressure to the branch conduit IS. The fan motor is stopped so that the cold air in the refrigeration chamber will not continue to chill the evaporator surfaces after the refrigerating function ceases, and to prevent the air in the refrigerated chamber being warmed as the evaporator warms up during defrosting. The electric heater is energized and the solenoid valve Zii is opened, permitting gaseous refrigerant to flow through the branch conduit I8 into the tubes of the evaporator. At the end of the period of defrosting, the functions of the defrost control are reversed, the fan being started, the electric heater cut off, and the motor of the compressor stopped, unless the temperature of the refrigerated chamber as sensed by the thermostatic bulb 24, requires the compressor to remain in operation. During the defrosting period the hot gas in that portion of the branch conduit which parallels the discharge pipe 4 keeps the latter open so that there is complete drainage of the defrost water from the system.

The T-fitting 25, by means of which the branch conduit I8 is connected into the pipe I5, is formed with a partition 25, having an orifice 21 drilled therethrough (see Figure 2), said orifice being carefully sized according to the refrigerating capacity of the particular evaporator with which it is used, to control the amount of hot gas entering the evaporator. The size of the orifice is such as to restrict the flow of gaseous refrigerant into the evaporator so that no more can be condensed into liquid than can be evaporated by the ascending column of hot gas in the branch conduit as the condensed liquid drains back through said branch conduit in contrafiow direction to the hot gas. By this simple means, it is impossible for any refrigerant to reach the compression chamber of the compressor in liquid form. Other forms of orifice than that shown are within the purview of the invention.

Since the amount of accumulated frost on the exterior surfaces of the evaporator may vary with the nature of the product being kept under refrigeration, it is contemplated that the timer may be set to vary the length of the defrosting periods so as to assure complete defrosting of the evaporator.

While I have in the above description disclosed what I believe to be a preferred and practical embodiment of the invention, it will be understood by those skilled in the art that the specific details of construction and arrangement of parts, as shown, are by way of illustration and not to be construed as limiting the scope of the invention.

What I claim is:

1. Refrigeration system for maintaining a refrigerated chamber at a temperature below 32 F., comprising means forming a refrigerated chamber, and within said chamber the following elements of said system, an evaporator, a pan for defrost water below said evaporator having a discharge opening, a drain pipe extending from said opening to a point without said chamber and a baffle in said pan beneath said evaporator sloping downward toward said discharge opening, a compressor, condenser, and receiver outside of said refrigerated chamber having the usual suction line from the low side of said compressor to the upper part of said evaporator, the hot gas line from the high side of said compressor to said condenser and the liquid line from said receiver to the lower part of said evaporator including an expansion valve adjacent said evaporator, means for defrosting said evaporator by hot gaseous refrigerant comprising a conduit connection from said hot gas line to the lower part of said evaporator, said conduit connection being in heat exchange proximity to said drain pipe, a normally closed valve controlling the passage of hot gaseous refrigerant through said conduit connection, an electric heater for heating said baffle, timer controlled means for periodically opening said valve and activating said heater, and means providing a fixed orifice in said conduit connection so calibrated with respect to the capacity of the system with which it is employed as to limit the rate of flow of hot gaseous refrigerant to said evaporator to the extent that it cannot condense in sufficient quantity to slug over into said suction line or in greater amount than will be completely evaporated by the hot gas in said conduit connection while draining back within said connection.

2. Refrigeration system comprising means forming a refrigerated chamber and within said chamber the following elements of said system, an evaporator, a pan for defrost water below said evaporator having a discharge opening, a drain pipe extending from said opening to a point outside of said chamber, a compressor, condenser and receiver outside of said refrigerated chamber having the usual suction line from the low side of said compressor to the upper part of said evaporator, the hot gas line from the high side of said compressor to said condenser, the liquid line from said receiver to the lower part of said evaporator including an expansion valve adjacent said evaporator, means for defrosting said evaporator by hot gaseous refrigerant comprising a conduit connection from said hot gas line to said liquid line at a point between said expansion valve and evaporator, said conduit connection being in heat exchanging proximity to said drain pipe, a defrosting valve in said conduit connection normally closed when said system is in its freezing cycle, means for opening said valve periodically to effect defrosting, and means providing an orifice of fixed size within said conduit connection between said evaporator and defrosting valve permanently determining a constant maximum rate of flow through said branch conduit, so calibrated with respect to the capacity of the system with which it is employed as to limit the rate of flow of hot gaseous refrigerant to said evaporator to the extent that it cannot condense in safe quantity to slug over into said suction line or in greater amount than will be completely evaporated by the hot gas in said conduit connection while draining back within said connection.

3. In a refrigeration unit, a compressor, condenser, receiver, evaporator, expansion valve, and the usual suction line from the evaporator to the low side of the compressor, the hot gas line from the high side of the compressor to the condenser, the liquid line from the receiver to the expansion valve, and the connection from the expansion valve to the evaporator, means for defrosting the evaporator comprising a branch conduit from said hot gas line to the connection between said expansion valve and evaporator, a defrosting valve in said branch conduit normally closed when said unit is in its freezing cycle, means for opening said valve periodically to effect defrosting, and means providing an orifice of fixed size within said branch conduit between said evaporator and said defrosting valve permanently determining a constant maximum rate of flow through said branch conduit, so calibrated with respect to the capacity of the system with which it is employed as to limit the rate of flow of hot gaseous refrigerant to said evaporator to the extent that it cannot condense in suflicient quantity to slug over into said suction line or in greater amount than will be completely evaporated by the hot gas in said conduit connection while draining back within said connection.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 530,494 Church et a1 Dec. 4, 1894 2,451,385 Groat Oct. 12, 1948 2,463,027 Frie Mar. 1, 1949 2,526,379 Maseritz Oct. 17, 1950 

